On single-track railway lines, a token system is used as a safety mechanism to prevent collisions by ensuring that only one train occupies a given section of track at any time. This system involves the physical exchange of a token, often mounted in a leather pouch or a “hoop”, between station staff and the train driver.
The token itself is not just a symbol of permission; it is typically part of an electrically interlocked system where keys at either end of the track are linked by wire to ensure mutual exclusivity. Only when both keys are inserted into the machines can one be withdrawn, granting a single train access to the line. Once a key is removed, the machines lock out further access, signaling that the section is occupied.
This failsafe, mechanical-electrical system prevents human error from compromising safety. If a token were to be lost or dropped, strict railway protocols would halt all train movement until the token is recovered or replaced, ensuring the integrity of the single-line control remains uncompromised.
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